Three-dimensional (3D) television has been a technology trend in recent years that intends to bring viewers sensational viewing experience. Various technologies have been developed to enable 3D viewing and the multi-view video is a key technology for 3DTV application among others. For 3D coding, depth maps are also coded along with the texture data.
In 3D-HEVC, partition-based methods are applied for depth map Intra coding. The partition-based methods use depth map modelling (DMM) to form prediction of the current depth block based on reconstructed neighboring depth pixels. With partition-based depth map Intra coding methods, a depth block is partitioned into two segments, named as P0 and P1 in the examples of FIG. 1. Each segment is represented by a single constant value, also called a DC value. In FIG. 1, DC values, DC0 and DC1 are selected for segments P0 and P1 respectively. For depth map Intra coding, a delta DC/residual value is determined and explicitly signalled in the bitstream so that reconstructed depth maps can be formed according to the DC values and the transmitted delta DC/residual value.
In the current 3D-HEVC development, DMM prediction partition a depth block into two segments according to four partition patterns, also called “cases” as shown in FIG. 2. The dmm prediction cases are described in the following pseudo codes.                bT=(bPattern0,0!=bPatternN−1,0)? 1:0; and        bL=(bPattern0,0 !=bPattern0,N−1)? 1:0,where bPatternX,Y represents the segment number of sample (X,Y), bPatternX,Y=0 if the sample at (X,Y) is in segment 0, and bPatternX,Y=1 if the sample at (X,Y) in segment 1. As shown in the above equations, bT is an indication that the two ending depth samples in the top row of the current depth block are not in the same segment, and bL is an indication that the two ending depth samples in the left column of the current depth block are not in the same segment. The four cases of DMM prediction mode are determined as follows.        Case 1: bT==bL && bL==1,                    DCX=(p−1,0+p0,−1)>>1, and            DC1−X=(p−1,N−1+pN−1,−1)>>1.                        Case 2: bT==bL && bL==0,                    DCX=(p−1,0+p0,−1)>>1, and            DC1−X=2B−1, where B represents the bit depth.                        Case 3: bT !=bL && bL==1,                    DCX=p(N−1)>>1,−1, and            DC1−X=p−1,N−1.                        Case 4: bT !=bL && bL==0,                    DCX=p−1,(N−1)>>1, and            DC1−X=pN−1,−1.                        
As shown in FIG. 2, both case 1 and case 2 have similar partition patterns. However, segment 0 in case 2 covers the entire top row and left column. In this case, segment 1 in case 2 is filled by a DC value corresponding to half of the maximum depth value (i.e. 2B/2). For case 1, segment 0 does not cover the entire top row and does not cover the entire left column. Segment 1 in case 1 is filled by a DC value derived from p−1,N−1 and pN−1,−1. For segment 0, the DC value is determined from p−1,0 and p0,−1 in the same way for both case 1 and case 2.
It is desirable to simplify the depth Intra prediction process without noticeable impact on the performance.